Today's cellular communication systems provide not only voice services, but also mobile broadband services all over the world. As the number of applications for cell phones and other wireless devices continues to increase, and consume higher ever-increasing amounts of data, an enormous demand for mobile broadband data services is generated. This requires telecom operators to improve data throughput and maximize the efficient utilization of limited resources.
In response to the fact that the spectrum efficiency for the point-to-point link is already approaching its theoretical limit, the telecom industry has introduced the concept of a multi-layered network in order to fulfil the growing demands for mobile broadband data services. Generally, a multi-layered network consists of several layers of base stations that provide or enable different physical resources such as frequency bandwidth, transmit power, etc. to provide broadband data services. A heterogeneous network is one example of a typical two-layered network where a macro layer consisting of high transmit power base stations is complemented with another low transmit power node (LPN) layer using at least one common carrier. Another example of a heterogeneous network is when a macro layer is complemented with another layer of low transmit power nodes that provide communications using a different frequency carrier than the macro layer nodes.
There are many challenges to achieving a working multi-layer network and integrating the multiple layers of the network. For a non-limiting example, one consequence of deploying a multi-layered network is that the density of the sites is much higher than otherwise required. Some significant challenges are addressing the current physical cell identity (PCI) conflict or confusion and enabling efficient operation among different layers by developing more efficient cell discovery mechanisms, etc. In the non-limiting example of a highly dense multi-layered network, the current mechanism operates extremely inefficiently, both for inter-layer and intra-layer networks. One of the inefficiencies is caused by the power consumption of handsets.
In the non-limiting example of a cellular mobile network, a PCI is usually carried in the synchronization channels and it is used in many control messages related to the mobility management. For example, when a user equipment (UE) detects a better cell than the current one, it sends a measurement report containing the PCI of the detected cell. Due to its frequent use, a PCI is defined locally instead of globally in order to reduce its signaling overhead. Therefore, PCI is only distinguishable within a limited number of neighboring cells, and is the basis for Auto-Neighbor-Relationship (ANR) in a Self Organizing Network (SON). In a Long-Term Evolution (LTE) network, for example, PCI is denoted by the primary synchronization signal (PSS) index {0,1,2} and the secondary synchronization signal (SSS) index {0, 1, . . . , 167}. Thus, there are 3*168=504 distinguishable PCIs in total. Since there are a limited number of PCI's, as the network becomes more dense, e.g., by adding more LPNs, there would be a situation in which a base station has neighboring cells with duplicate PCI's. Thus, it is unable to determine the correct target cell for handover from the PCI included in the measurement reports from the UE. Although this can be solved by instructing the UE to report the corresponding global ID, this method not only consumes more signaling resources over the air, but also degrades the mobility performance.